The present invention relates to an optical illuminating device for use in a copying apparatus for illuminating the original to be copied on a sheet of copying material.
A diversity of copying machines, whatever type of copying process they employ, are now commercially available. Most of the commercially available copying machines are bulky and the recent trend in the concern of the related industry is development of relatively small-sized copying machines. Though there are numerous methods of reducing the size of a copying machine, one of the relatively small-sized copying machines that have heretofore been developed employs for its optical system an image transmitter composed of a plurality of SELFOC (a trademark registered in Japan and owned by Nippon Sheet Glass Co., Ltd.) lenses in a bundled configuration.
The SELFOC lens refers to an image transmitting optical fiber made of glass or synthetic resin and having a refractive index distribution in a cross section thereof that varies consecutively and parabolically outwards from a center portion thereof, such refractive index distribution satisfying the following equation; n = N(1 - ar.sup.2), wherein N is a refractive index at the center, n is a refractive index at a distance r from the center and a is a positive constant. The SELFOC lens and the image transmitter formed by a bundle of SELFOC lenses are described in the U.S. Pat. No. 3,658,407, patented on Apr. 25, 1972, and therefore, reference may be made thereto for the details thereof.
In the copying machine wherein the optical system utilizes the particular image transmitter composed of the SELFOC lenses bundled side by side by the use of an adhesive material, the inventor has found that a great amount of light can enter the particular image transmitter avoiding to increase flared light if a beam of light travelling towards a transparent support for supporting thereon the original to be copied impinges upon the transparent support at an angle of incidence in the vicinity of 45.degree.. Accordingly, in the case where the particular image transmitter is to be employed during manufacture of a copying machine for the purpose of reducing the size of the resultant copying machine, the particular image transmitter has to be arranged in position to satisfy the above mentioned particular and, in addition thereto, an optical illuminating device capable of emitting a relatively large amount of light has to be employed in the copying machine. Both of these requrements are important factors to be taken into consideration in order to manufacture a copying machine in a size as compact as possible.
According to the prior art, a copying machine wherein the optical illumination is designed such as shown in FIG. 1 is provided. Referring to FIG. 1, the optical illumination device comprises a single elliptical reflector M having a concave, reflective wall M.sub.1 which comprises a portion of the wall of a hollow right elliptical cylinder such as shown by C in a broken curved line. The right elliptical cylinder C has two imaginary parallel line foci A.sub.1 and A.sub.2 and a line light source L, for example, a tubular electrical lamp, is disposed in a position with the longitudinal axis thereof in alignment with one of theline foci A.sub.1, the other line focus A.sub.2 being parallelly occupied by one of the surfaces of a transparent support 4 on which the original P to be copied is stationarily placed. In practice, the position of the line focus A.sub.2 relative to the transparent support 4 is adjusted, in consideration of the presence of a particular refractive index of a transparent glass material forming the transparent support 4, by a shade 3 positioned such that the angle of incidence can be in the vicinity of 45.degree..
In the prior art copying machine of the arrangement as hereinbefore described, light emitted from the tubular light source L and after having been reflected by the concave wall M.sub.1 illuminates an elongated portion of the original P placed on the transparent support 4, which elongated portion is schematically indicated by B and is to be understood as extending in a direction at right angles to the plane of the drawing of FIG. 1. The light having impinged upon the original P and reflected therefrom in a substantially slit-like configuration is subsequently projected through the particular image transmitter 1 onto a light sensitive sufrace 2 on which an image of the original P is exposed, light sensitive surface 2 being either a copying material itself or a known photoreceptor.
In the prior art arrangement so far described, since the light source L is positioned relatively close to the particular image transmitter 1, some or all of the optical fibers forming the particular image transmitter 1 and/or an adhesive material used to bundle the optical fibers to provide the particular image transmitter 1 tend to be softened by the heat of the light source L so that the performance characteristics of the particular image transmitter is adversely affected. In addition, it has been found that the support 4 and/or the particular image transmitter 1 are deteriorated in quality and that, since the amount of light which illuminates the elongated portion of the original P is defined by light reflected from an elongated portion of the concave wall M.sub.1 between a pair of parallely spaced line positions T.sub.1 and T.sub.2 which appear as points in FIG. 1 because of the cross sectional representation of the illumination device, it is relatively small.